CN110565113A - Preparation method of composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution - Google Patents

Abstract

A preparation method of a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution, the method grows one deck of Ni(OH) on carbon fiber paper ₂ nanosheet structure; vacuum electroplating an oxide layer coated with titanium on its surface; Then placed in a muffle furnace at a temperature of 360 degrees under an air atmosphere to anneal and crystallize to obtain a TiO ₂ ‑Ni(OH) ₂ @CFP composite structure material; the TiO ₂ ‑Ni(OH) ₂ @CFP is controlled under vacuum conditions. Composite electrocatalytic materials after different coating times were obtained after annealing and crystallization in air atmosphere. The present invention uses CFP as the substrate material of the catalyst, which increases the surface area of the composite electrode, facilitates mass transfer and improves the electrochemical activity of the electrode; at the same time, Ni(OH) ₂ grown on the substrate material by hydrothermal reduces the cost and enables Ni(OH) ₂ is more firmly combined with the substrate material, and the uniform distribution improves the stability of the catalyst. The introduction of TiO ₂ in the present invention plays a great role in improving the catalytic performance of the catalyst and reducing the hydrogen evolution overpotential; and realizes the remarkable improvement of the electrocatalytic hydrogen evolution activity.

Description

A preparation method of composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution

technical field

The invention relates to a preparation method of a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution, belonging to the technical field of electrocatalysis.

Background technique

The excessive consumption of fossil resources and the resulting environmental pollution force us to develop and utilize renewable clean energy that can replace fossil fuels. As a clean, efficient, safe and sustainable new energy, hydrogen energy is regarded as the most promising clean energy in the 21st century. Hydrogen production by electrolysis of water is an effective way to solve the current dilemma. However, the existence of overpotential in the process of water electrolysis leads to high energy consumption in electrolysis of water. Therefore, we need to develop highly active hydrogen evolution reaction catalysts to reduce the overpotential of water splitting reaction, thereby improving energy conversion efficiency. Ideal water electrolysis should produce hydrogen at low cost and high yield, but since the most effective electrocatalysts for efficient hydrogen production are still dominated by scarce and expensive noble metal-based materials (e.g., Pt for HER), this is not true. It is conducive to large-scale application in industry. Therefore, there is an urgent need to develop water electrolysis catalysts with low overpotential and earth-abundant reserves to improve the reaction kinetics and water electrolysis efficiency. Most of the current HER electrocatalysts are more efficient in acidic conditions than in alkaline conditions, because the HER process of electrocatalysts is less efficient in alkaline media, which is related to the slow dissociation process of water on the surface of the electrocatalyst, but the electrolysis of water in alkaline Alkaline electrolytes have the advantages of easy availability and long-lasting performance when carried out in electrolyzers. However, the current research on promoting water dissociation in alkaline electrolytes has increased, but the performance of synthesized composites is still unsatisfactory. , and there is still a large gap compared with noble metal-based electrocatalysts, so the development of high-performance electrocatalysts is still a great challenge.

Nickel-based layered hydroxide has a controllable composition and structure. It has been continuously proved by researchers that its electrolytic water activity has been improved after being combined with other materials. The nickel-based layered hydroxide has poor electrocatalytic hydrogen evolution performance. Poor stability, short service life, poor conductivity, difficult recycling, high cost of raw materials for preparation, and relatively large environmental pollution during the preparation process need to be solved urgently. An electrocatalyst with excellent performance should have a moderate hydrogen ion adsorption capacity. _TiO2 can promote the adsorption and dissociation of water molecules on its surface, and the hydrogen intermediate produced by the dissociation will be transported from the surface of titanium oxide to the surface of the electrocatalyst through the overflow effect, thereby Improve the hydrogen evolution catalytic activity of the loading system.

Contents of the invention

The purpose of the present invention is to prepare a catalyst suitable for hydrogen evolution reaction in alkaline electrolyte, improve the catalytic performance of the catalyst, and ensure the rapid and efficient hydrogen production by electrolysis of water. The present invention provides a catalyst for alkaline electrocatalytic hydrogen evolution Preparation method of composite electrocatalytic material.

In order to solve the above technical problems, the present invention adopts the following technical scheme: a method for preparing a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution, the composite electrocatalytic material prepared by the method is TiO ₂ -Ni(OH) ₂ @ CFP composite structural material.

The preparation method of the composite structural material is as follows: first grow a layer of Ni(OH) ₂ nanosheet structure on the carbon fiber paper; then vacuum electroplate an oxide layer coated with titanium on its surface to obtain titanium dioxide-coated Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor; then placed in a muffle furnace at a certain temperature in the air atmosphere for annealing and crystallization to obtain a TiO ₂ -Ni(OH) ₂ @CFP composite structure material; the TiO ₂ -Ni(OH) ) ₂ @CFP Under vacuum conditions, control different coating times, and anneal and crystallize in air atmosphere to obtain composite electrocatalytic materials after coating at different times are TiO ₂ -Ni(OH) ₂ @CFP-XXX, where XXX=20 , 40, 80 or 120 minutes.

TiO ₂ -Ni(OH) ₂ @CFP-20, TiO ₂ -Ni(OH) ₂ @CFP-40, TiO ₂ -Ni(OH) ₂ @CFP-80, TiO ₂ -Ni(OH) ₂ @CFP- 120 are film-coated composite electrocatalysts at different times, respectively.

The TiO ₂ -Ni(OH) ₂ @CFP composite structure material has a layered structure morphology, its primary structure is Ni(OH) ₂ nano flakes, and the thickness of the flakes is 20-40nm.

The preparation method steps of the TiO ₂ -Ni(OH) ₂ @CFP-XXX composite electrocatalytic material are as follows:

(1) Preparation of Ni(OH) ₂ .nH ₂ O nanosheets on carbon fiber paper

Add 0.725 g of Ni(NO ₃ ) ₂ ·6H ₂ O, 0.185 g of NH ₄ F and 0.625 g of CO(NH ₂ ) ₂ into 40 ml of water, stir rapidly until completely dissolved, then continue stirring for 10 minutes to obtain a mixed solution , then place 3×2cm ² carbon fiber paper horizontally on the bottom of the reaction kettle, add the mixed solution, react at 130°C for 12 hours, cool to room temperature after the reaction, wash with deionized water and absolute ethanol, and dry at 80°C for 6h, Light green Ni(OH) ₂ .nH ₂ O nanosheets are uniformly covered on the surface of nickel foam;

(2) TiO2-coated Ni(OH) ₂ .nH ₂ O nanoflakes

Take the light green Ni(OH) ₂ .nH ₂ O nanosheets synthesized in step (1) and place them in a vacuum coating machine, spray the sublimation plating solution, and adjust the spraying time to 20, 40, 80, and 120 minutes respectively; the reaction is over Afterwards, vacuum-dry at 60°C for 6 hours to obtain the Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor coated with titania;

(3) Take the carbon fiber paper sample loaded with titanium dioxide-coated Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor in step (2), place it in a muffle furnace for annealing and crystallization, and obtain TiO ₂ -Ni(OH) ₂ @CFP-XXX composite catalytic materials.

The molar ratio of Ni(NO ₃ ) ₂ ·6H ₂ O, NH ₄ F and CO(NH ₂ ) ₂ is 1:2:5.

In step (1), the reaction is carried out in a polytetrafluoroethylene-lined reactor with a capacity of 100 milliliters, and the filling degree is 50-60% by volume.

In step (2), the sublimation plating solution is butyl titanate and distilled water, and the vacuum degree is 30 Pa; the butyl titanate and distilled water are alternately sublimated.

In step (3), during the annealing and crystallization process, the annealing temperature is 360°C, the holding time is 2h, and the heating rate is 5°C/min ^-1 .

The composite structure electrocatalyst prepared by the method has an overpotential of 335mV at a current density of 20mA/cm ^-2 , and has good electrocatalytic activity; after 45 hours of electrocatalysis, it still maintains more than 90% of the catalytic activity.

The titanium dioxide-coated Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor is annealed and crystallized at 360°C in an air atmosphere; after annealing, the amorphous TiO ₂ crystallizes into a sharp crystal that can improve catalytic performance. Titanite type, the precursor nickel hydroxide containing crystal water loses water and transforms into nickel hydroxide.

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

(1) The preparation method of the electrocatalytic material of the present invention adopts the hydrothermal method and the vacuum sublimation coating method to prepare TiO ₂ -Ni(OH) ₂ @CFP, not only the preparation conditions are easy to control, but also the Ni(OH)2 is loaded in the form of nano flakes On the CFP, the surface area of the electrode material is increased, and the electrocatalytic activity of the electrode is promoted; the use of the vacuum coating method, the coating is uniform and firm, and the thickness of the coating is controllable;

(2) The present invention adopts CFP as the base material of catalyst, because the structure characteristic of CFP in network shape increases the surface area of composite electrode, then helps mass transfer and improves the electrochemical activity of electrode; The grown Ni(OH) ₂ reduces the cost and makes the combination of Ni(OH) ₂ and the base material stronger, and the uniform distribution improves the stability of the catalyst.

(3) The introduction of TiO ₂ in the present invention has played a great role in improving the catalytic performance of the catalyst and reducing the hydrogen evolution overpotential, due to the d electron interaction between TiO ₂ and Ni has changed the electronic structure of Ni, and at the same time strengthened the catalyst Significant improvement in electrocatalytic hydrogen evolution activity can be achieved by absorbing water molecules.

Description of drawings

Fig. 1 is the X-ray diffraction spectrum of the composite electrocatalyst sample prepared according to the method for embodiment;

Fig. 2 is the SEM figure and the EDS element map of the sample prepared according to the method for comparative example and embodiment;

Among them, Figure 2(a) is a low-magnification scanning electron microscope, Figure 2(b-c) is a high-power scanning electron microscope, Figure 2(d-g) is a SEM image and an EDX element map, Figure 2(e) is an oxygen element, and Figure 2(f ) is a nickel element, Fig. 2 (g) is a titanium element, and Fig. 2 (h) is an EDS elemental analysis diagram;

Fig. 3 is the overpotential curve figure of the sample prepared according to the method for comparative example and embodiment;

Fig. 4 is the Nyquist curve of the sample prepared according to the method of comparative example and embodiment;

Fig. 5 is the stability test of the sample prepared according to the method for comparative example and embodiment;

Figure 6 is the preparation process of the composite electrocatalyst for alkaline electrocatalytic hydrogen evolution.

Detailed ways

The specific implementation steps of the present invention are shown in FIG. 6 .

The raw materials used in this example are Ni(NO ₃ ) ₂ , NH ₄ F, CO(NH ₂ ) ₂ .

Weigh 0.725 g of Ni(NO ₃ ) ₂ 6H ₂ O, 0.185 g of NH ₄ F and 0.625 g of CO(NH ₂ ) ₂ and stir quickly until completely dissolved, then continue stirring for 10 min to obtain a mixed solution, mix and dissolve in 40 ml of water;

Then take a piece of carbon fiber paper (CFP) and cut it into a block with an area of 2×3cm ² , ultrasonically clean it in acetone, ethanol and water for 15 minutes respectively, take it out and weigh it dry;

Then pour the above solution into the inner tank of a 50mL reaction kettle, and add a piece of washed 2×3cm ² CFP, seal the reaction kettle and keep the temperature at 130°C for 12 hours, wash with deionized water and absolute ethanol, and place at 80 Dry at ℃ for 6 hours, and weigh the mass of the precursor loaded on the carbon fiber paper;

Take the light green Ni(OH) ₂ .nH ₂ O nanosheets synthesized in the above steps and place them in a vacuum coating machine. The sublimation plating solution is butyl titanate, and the spraying time is adjusted to 20, 40, 80, and 120 minutes respectively. ; after the reaction, vacuum drying at 60° C. for 6 hours to obtain a Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor coated with titanium dioxide;

Take the carbon fiber paper sample synthesized above loaded with titanium dioxide-coated Ni(OH) ₂ .nH ₂ O nanoflakes, place it in a muffle furnace for annealing and crystallization at 360°C for 2 hours, and weigh Measure the load.

For the sample obtained in the embodiment, the diffraction data were measured by X-ray diffraction method, as shown in FIG. 1 . The curve in Figure 1 is the diffraction data obtained by testing the prepared composite electrocatalyst samples. The vertical lines in Figure 1 are standard card data.

It can be seen from Figure 1 that the sample is indexed, its space group is P-3m1, and its lattice constant is a=b=3.126, α=β=90°, γ=120°. There is no change in the lattice constant and no impurity phase, indicating that TiO ₂ is incorporated into the compound in a small amount and does not reflect its crystal phase.

For the sample obtained in the embodiment, the new appearance of the sample was measured by SEM scanning, and the elemental composition data was measured by energy dispersive X-ray spectroscopy (EDS), as shown in FIG. 2 .

Figure 2 shows that TiO ₂ -Ni(OH) ₂ @CFP nanoflakes are homogeneously deposited on the surface of CFP, and the thickness of a single nanosheet on the surface of CFP is about 20-30nm. Energy dispersive X-ray spectroscopy (EDS) confirmed the presence of Ni, Ti, and O in TiO ₂ -Ni(OH) ₂ @CFP.

The overpotential curves of the samples of the comparative examples and the examples are shown in FIG. 3 .

The overpotential at -20mA/cm ² is usually used for comparison. Obviously, the absolute value of the overpotential of the sample coated with TiO ₂ layer is much smaller than that of the control sample without TiO ₂ layer. The hydrogen evolution overpotential of the uncoated TiO ₂ layer sample exceeds 500mV under alkaline conditions, and the absolute value of the overpotential of the electrocatalyst sample coated with the TiO ₂ layer for 80 minutes decreases to 335mV, which has the best electrocatalytic hydrogen evolution performance.

The Nyquist curves of the samples of the comparative example and the example are shown in FIG. 4 .

The semicircle in the low-frequency range is related to the Faradaic process (HER) occurring on the surface of the electrocatalyst. Its corresponding resistive component is the charge transfer resistance (R _ct ).

R _ct is often used to evaluate the kinetic process of HER. Generally, the smaller the R _ct is, the faster the HER process is. Obviously, R _ct decreases after Ni(OH) ₂ nanosheets are coated with TiO ₂ , which indicates that TiO ₂ -Ni(OH) ₂ @CFP nanosheets have the fastest electron transfer ability in hydrogen evolution reaction.

Electrocatalytic performance test of materials:

The electrochemical test adopts a three-electrode system, which is tested by the CHI-614D electrochemical analyzer workstation. The CFP loaded with catalyst is used as the working electrode, the carbon rod electrode is used as the counter electrode, and the silver/silver chloride electrode (Ag/AgCl) is used as the reference electrode. . Electrochemical test electrolyte is 1mol/L KOH solution, and argon gas is passed through the solution for 10 minutes before the test to remove the air in the electrolyte.

The experimental results show that the current density can reach 20mA/cm ^-2 when the overpotential of electrocatalytic hydrogen evolution is 335mV.

Stability test:

The electrochemical test adopts a three-electrode system, which is tested by the CHI-614D electrochemical analyzer workstation. The CFP loaded with catalyst is used as the working electrode, the carbon rod electrode is used as the counter electrode, and the silver/silver chloride electrode (Ag/AgCl) is used as the reference electrode. . Electrochemical test electrolyte is 1mol/L KOH solution, argon gas is passed through the solution for 10 minutes before the test to remove the air in the electrolyte, and the stability test maintains a constant voltage of 750mV. The product has good stability. Under a constant voltage of 750mV, the current density does not decrease by more than 5% within 40 hours, and the structure is stable without collapse.

Claims (9)

1. A method for preparing a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution, characterized in that the composite electrocatalytic material prepared by the method is a TiO ₂ -Ni(OH) ₂ @CFP composite structure material, The preparation method of the composite structural material is as follows: growing a layer of Ni(OH) ₂ nanosheet structure on carbon fiber paper; vacuum electroplating an oxide layer coated with titanium on its surface to obtain titanium dioxide-coated Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor; then placed in a muffle furnace at a certain temperature under an air atmosphere for annealing and crystallization to obtain a TiO ₂ -Ni(OH) ₂ @CFP composite structure material; the TiO ₂ -Ni(OH) ₂ @CFP Under vacuum conditions, control different coating times, and anneal and crystallize in air atmosphere to obtain composite electrocatalytic materials after coating at different times are TiO ₂ -Ni(OH) ₂ @CFP-XXX, where XXX=20,40 , 80 or 120 minutes; TiO ₂ -Ni(OH) ₂ @CFP-20, TiO ₂ -Ni(OH) ₂ @CFP-40, TiO ₂ -Ni(OH) ₂ @CFP-80, TiO ₂ -Ni(OH) ₂ @CFP- 120 are film-coated composite electrocatalysts at different times, respectively. 2. A method for preparing a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution according to claim 1, wherein the TiO ₂ -Ni(OH) ₂ @CFP composite structure material is a layered structure Morphology, its primary structure is Ni(OH) ₂ nano flakes, the flake thickness is 20-40nm. 3. A method for preparing a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution according to claim 2, wherein the TiO ₂ -Ni(OH) ₂ @CFP-XXX composite electrocatalytic material The preparation method steps are as follows: (1) Preparation of Ni(OH) ₂ .nH ₂ O nanosheets on carbon fiber paper Add 0.725 g of Ni(NO ₃ ) ₂ ·6H ₂ O, 0.185 g of NH ₄ F and 0.625 g of CO(NH ₂ ) ₂ into 40 ml of water, stir rapidly until completely dissolved, then continue stirring for 10 minutes to obtain a mixed solution , then place 3×2cm ² carbon fiber paper horizontally on the bottom of the reaction kettle, add the mixed solution, react at 130°C for 12 hours, cool to room temperature after the reaction, wash with deionized water and absolute ethanol, and dry at 80°C for 6h, Light green Ni(OH) ₂ .nH ₂ O nanosheets are uniformly covered on the surface of nickel foam; (2) TiO2-coated Ni(OH) ₂ .nH ₂ O nanoflakes Take the light green Ni(OH) ₂ .nH ₂ O nanosheets synthesized in step (1) and place them in a vacuum coating machine, spray the sublimation plating solution, and adjust the spraying time to 20, 40, 80, and 120 minutes respectively; the reaction is over Afterwards, vacuum-dry at 60°C for 6 hours to obtain the Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor coated with titania; (3) Take the TiO2-coated Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst precursor in step (2), place it in a muffle furnace for annealing and crystallization, and obtain TiO ₂ -Ni( OH) ₂ @CFP-XXX composite catalytic material. 4. A kind of preparation method for the composite electrocatalytic material that is used for alkaline electrocatalytic hydrogen evolution according to claim 3, is characterized in that, described Ni(NO ₃ ) ₂ 6H ₂ O, NH ₄ F and CO( The molar ratio of NH ₂ ) ₂ is 1:2:5. 5. A kind of preparation method for the composite electrocatalytic material that is used for alkaline electrocatalytic hydrogen evolution according to claim 3, is characterized in that, in step (1), described reaction is in the capacity of 100 milliliters polytetrafluoroethylene It is carried out in a lined reactor with a filling degree of 50-60% volume ratio. 6. a kind of preparation method for the composite electrocatalytic material that is used for alkaline electrocatalytic hydrogen evolution according to claim 3, is characterized in that, in step (2), described sublimation bath is butyl titanate and distilled water, The vacuum degree is 30 Pa; the butyl titanate and distilled water are alternately sublimated. 7. A method for preparing a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution according to claim 3, characterized in that, in step (3), during the annealing and crystallization process, the annealing temperature is 360°C , holding time 2h, heating rate 5℃/min ^-1 . 8. A kind of preparation method for the composite electrocatalytic material that is used for basic electrocatalytic hydrogen evolution according to claim 2, it is characterized in that, the composite structure electrocatalyst that described method prepares under the electric current density of 20mA/cm ^-2 The overpotential is 335mV, which has good electrocatalytic activity; after 45 hours of electrocatalysis, it still maintains more than 90% of the catalytic activity. 9. A method for preparing a composite electrocatalytic material for alkaline electrocatalytic hydrogen evolution according to claim 3, characterized in that the titanium dioxide-coated Ni(OH) ₂ .nH ₂ O nanosheet electrocatalyst The precursor is annealed and crystallized at 360°C in an air atmosphere; after annealing, the amorphous TiO ₂ is crystallized into anatase type that can improve catalytic performance, and the nickel hydroxide containing crystal water in the precursor loses water and transforms into hydroxide nickel.