Special vulcanized CoFe prussian blue as well as preparation and application thereof

Abstract

The invention discloses a specially vulcanized CoFe prussian blue as well as preparation and application thereof. The porous three-dimensional graded non-noble metal sulfide catalyst is prepared by taking a ferrocobalt Prussian blue analogue as a template through calcination treatment and vulcanization. The catalyst is of a cubic porous structure, has high porosity and good conductivity, and has excellent hydrogen evolution and oxygen evolution electrocatalytic activity in an alkaline medium. The invention aims to provide a Prussian-blue-like electrocatalyst subjected to special vulcanization, the Prussian-blue-like electrocatalyst is used as a working electrode for an electrochemical test, the result shows that the Prussian-blue-like electrocatalyst has good electrocatalytic activity, the OER overpotential is as low as 237 mV and the HER overpotential is 156 mV when the Prussian-blue-like electrocatalyst is 10 mA cm <-2 >, and the Prussian-blue-like electrocatalyst also shows good stability in an alkaline solution.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic synthesis and material preparation, and specifically to a special sulfided CoFe-based Prussian blue and its preparation and application, which is particularly suitable for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the electrocatalytic water decomposition reaction. Background Art

[0002] The continuous growth of the world's population and the advancement of science and technology have not only led to a shortage of traditional fossil fuels, but also brought many serious problems. Environmental pollution and energy crises are two major issues facing the world today. To this end, researchers around the world have begun to actively seek suitable green and renewable energy to replace traditional fossil fuels. Hydrogen is a clean energy with a high energy density. Its ultra-high specific energy density makes it suitable for use in high-energy fuel applications. Therefore, hydrogen energy is considered an ideal alternative to fossil energy.

[0003] Water electrolysis is currently the greenest and most efficient method for hydrogen production. This technology is carried out in an electrolyzer, where the hydrogen evolution reaction (HER) occurs at the cathode, generating hydrogen, while the oxygen evolution reaction (OER) occurs at the anode, generating oxygen. However, water electrolysis is kinetically slow, resulting in excessive overpotentials (the external voltage must exceed the thermodynamic equilibrium potential to a certain value for the reaction to occur). This leads to significant energy consumption, high costs, and inability to compete with traditional fossil fuel hydrogen production. Therefore, efficient electrocatalysts are needed to accelerate the reaction.

[0004] Prussian blue (PBA) and its analogs (PBAS), as coordination compounds, have greatly expanded their applications in various related fields due to their simple structure, facile preparation, rich diversity, controllable pore structure, and high specific surface area. The electrochemical performance of electrocatalysts is closely related to their composition and structure. The composition of a catalyst determines its activity and conductivity, and changes in the material morphology can expose more active sites. Therefore, when designing and preparing Prussian blue-derived materials, it is important to consider the composition, morphology, and structure to improve the catalytic performance of the catalyst. Summary of the Invention

[0005] The present invention aims to provide a specially sulfurized Prussian blue-like electrocatalyst that addresses the low activity and poor stability of existing non-precious metal catalysts. By manipulating the ratio of hydrazine hydrate to sulfur powder and the synthesis time, this material significantly improves its electrocatalytic activity and stability, making it suitable for hydrogen production by water electrolysis.

[0006] Further, the method specifically includes the following steps:

[0007] (1) Preparation of CoFe-PBA / NF: Weigh 0.1317 g of potassium ferricyanide and dissolve it in 20 ml of deionized water, denoted as solution A. Then weigh 0.2647 g of trisodium citrate and 0.1746 g of cobalt nitrate and dissolve them in 20 ml of deionized water, denoted as solution B. Pour solution A into solution B and stir vigorously for 10 minutes, then let it stand at room temperature for 18 hours.

[0008] (2) Preparation of CoFe-O / NF: Treat the precursor CoFePBA / NF in a muffle furnace at 350 °C with a heating rate of 2 °C / min for 2 hours.

[0009] (3) Preparation of CoFe-O-S / NF: Add 2 ml of hydrazine hydrate and 0.03 g of sulfur powder to the reaction kettle, mix and stir evenly, then put the prepared CoFe-O / NF into the reaction kettle, heat up to 140 °C and keep it for 24 hours. After cooling to room temperature, rinse it several times with ethanol and water, and dry it in an oven to obtain the sample.

[0010] Compared with the prior art, the advantages of the present invention are as follows:

[0011] The CoFe-based Prussian blue disclosed in the present invention is a kind of metal-organic framework material with unique structure and properties. Due to its high specific surface area, adjustable metal active sites and uniform catalytic centers, it has important significance for environmental protection and has good application prospects in electrocatalysis.

[0012] A preparation method of a special sulfided CoFe-based Prussian blue material disclosed in the present invention effectively removes water molecules and some CN groups in CoFe-PBA during the heat treatment process at 350 °C through appropriate heat treatment, resulting in the formation of CoFe alloy nanoparticles by the coordination of Co and Fe. Thereby improving its electrocatalytic performance. Finally, through a special sulfidation method, by controlling the ratio of hydrazine hydrate and sulfur powder, using Prussian blue analog (PBA) as the precursor, three-dimensional hierarchical cobalt-iron-based sulfide (CoFe-O-S) is prepared through hydrothermal sulfidation and calcination treatment. The results show that the mass ratio of PBA to the sulfur source, hydrothermal temperature, hydrothermal time and the presence of hydrazine hydrate are important factors for the formation of a mixed phase of Co8FeS8 and Ni3S2. These factors are beneficial to the rapid mass transfer and charge transfer in multiple directions, endow the material with mixed valence states, improve the electron conductivity and prevent the aggregation of nanostructured sulfides.

[0013] The optimized CoFe-O-S catalyst has good catalytic activity, and its overpotential for OER is 237 mV at 10 mA cm -2 and its overpotential for HER is 237 mV at 10 mA cm -2The overpotential is 156 mV. This study not only provides a simple and feasible method for preparing transition metal sulfides with excellent electrocatalytic activity, but also expands the synthesis and application of PBA-derived nanomaterials. Description of the Drawings

[0014] Figure 1 XRD patterns of CoFe-PBA / NF prepared in the present invention at different calcination temperatures;

[0015] Figure 2 XRD pattern of (O 350 / S 140 )CoFe-PBA / NF prepared in the present invention;

[0016] Figure 3 SEM image of (O 350 / S 140 )CoFe-PBA / NF prepared in the present invention under scanning electron microscope;

[0017] Figure 4 Polarization curves of CoFe-O / NF prepared in the present invention at different oxidation temperatures;

[0018] Figure 5 Polarization curves of CoFe-O-S / NF prepared in the present invention at different sulfidation temperatures;

[0019] Figure 6 Polarization curves of CoFe-O-S / NF prepared in the present invention at different sulfidation times;

[0020] Figure 7 Voltage-time curves of (O 350 / S 140 )CoFe-PBA / NF prepared in the present invention; Detailed Embodiments

[0021] To further understand the present invention, the present invention will be further described below in conjunction with the drawings and embodiments, but the present invention is not limited in any way.

[0022] Detailed Embodiment 1: An electrode material based on CoFe-O-S / NF as the working electrode for hydrogen production by electrolyzing water is formed by heat treatment and special sulfidation reaction of cobalt iron Prussian blue cubes;

[0023] Detailed Embodiment 2: The preparation method of an electrode material based on CoFe-O-S / NF as the working electrode for anodic oxygen evolution and cathodic hydrogen evolution in electrolyzing water is carried out according to the following steps:

[0024] I. Synthesis of CoFe-PBA / NF: Pretreatment of nickel foam: Cut the nickel foam into pieces with a size of 2×3 cm, then ultrasonicate it in hydrochloric acid, ethanol, and deionized water for 30 minutes each in sequence, rinse it thoroughly with deionized water, and air-dry it at room temperature for use. Take appropriate amounts of cobalt nitrate and sodium citrate, dissolve them in deionized water with vigorous stirring, and slowly add potassium ferricyanide to the mixed solution after complete dissolution. Continue stirring until it is dissolved, take it out after a certain period of time, rinse it, and dry it.

[0025] In step I, the masses of cobalt nitrate, sodium citrate, and potassium ferricyanide are respectively: 0.1746 g, 0.2647 g, and 0.1317 g;

[0026] The reaction conditions in step I are room temperature and 18 hours;

[0027] The drying conditions in step I are 60 °C and overnight;

[0028] II. Preparation of CoFe-O / NF: Heat-treat the precursor CoFe-PBA / NF in a muffle furnace. Different calcination temperatures are selected for comparison.

[0029] The oxidation temperatures in step II are 200 °C, 350 °C, and 500 °C;

[0030] III. Synthesis of CoFe-O-S / NF: Sequentially add hydrazine hydrate and sulfur powder into the reaction kettle, mix and stir evenly, then put the prepared precursor into the reaction kettle, heat up for sulfidation, cool it to room temperature, rinse it several times with ethanol and water, and dry it in an oven to obtain the sample. Different sulfidation temperatures and sulfidation times are selected for comparison to sulfidate CoFe-PBA.

[0031] In step III, the mass ratio of CoFe-PBA to sulfur powder is 1:10;

[0032] The sulfidation temperatures in step III are respectively 200 °C, 180 °C, 160 °C, 140 °C, and 120 °C, and the sulfidation time is 12 hours, 24 hours, and 36 hours;

[0033] IV. Preparation of electrolyzed water using the CoFe-O-S / NF electrode material as the working electrode: Prepare 100 mL of KOH with a certain concentration as the electrolyte, and take 20 - 30 mL for electrochemical testing. The CoFe-O-S / NF electrode material, carbon rod, and HgO electrode form a three-electrode system to test its OER and HER performance;

[0034] The concentration of KOH in step IV is 1.0 mol / L;

[0035] The CoFe-O-S / NF described in Step 4 is the working electrode, the carbon rod is the counter electrode, and HgO is the reference electrode; the size of the working electrode described in Step 4 is 1×1 cm.

[0036] The present invention will be further described below in conjunction with the drawings and embodiments:

[0037] (1) Characterize the synthesized different materials by X-ray diffraction (XRD):

[0038] As Figure 1 shown, by comparing the XRD pattern of the synthesized CoFe-PBA with the published literature, the positions of the diffraction peaks are the same, which proves that CoFe-PBA has been successfully prepared. After calcination treatment at a certain temperature, the peaks of CoFe-PBA have disappeared. As Figure 2 shown, after complete sulfidation, the positions of the main diffraction peaks of the generated CoFe-O-S / NF have obvious changes compared with CoFe-PBA. The original peaks of CoFe-PBA have completely disappeared and are all converted into the peaks of Co8FeS8 and Ni3S2 sulfides, indicating that the structure of the raw materials has changed and new substances have been generated;

[0039] (2) Characterize the morphology of the synthesized CoFe-O-S / NF by scanning electron microscope (SEM):

[0040] Figure 3 This is the SEM image of the CoFe-PBA prepared by the present invention under the scanning electron microscope. It can be observed that CoFe-PBA presents a cubic shape and is evenly distributed on the nickel foam. After complete sulfidation, it presents a nanosheet shape, indicating that the complete sulfidation of CoFe-PBA is successful.

[0041] (3) Test the polarization curves of the prepared different materials:

[0042] Figure 4 This is the OER and HER polarization curve graphs of CoFe-PBA at different oxidation temperatures. It can be observed that when the temperature is 350 °C, its performance reaches the best. Figure 5 It further shows that the performance reaches the best when the sulfidation temperature is 140 °C. By adjusting the sulfidation time, it can be observed that as Figure 6 shown, when the time is 24 h, the sulfidation is complete and the performance reaches the best state. Generally speaking, when the oxidation temperature is 350 °C, the sulfidation temperature is 140 °C, and the sulfidation time is 24 h, the overpotential of its OER is 237 mV at 10 mA cm -2 , and the overpotential of its HER is 156 mV at 10 mA cm -2 .

[0043] (4) For (O 350 / S 140)The stability of the CoFe-PBA / NF electrode material was tested:

[0044] Figure 7 For (O 350 / S 140 )CoFe-PBA / NF at 10 mA cm -2 The voltage-time curve at the current density. As Figure 7 shown, at a current density of 10 mA cm -2 Oxygen evolution continued for 20 h without a significant decrease, further indicating that (O 350 / S 140 )CoFe-PBA / NF has good stability.

Claims

1. A specially sulfided CoFe-based Prussian blue electrocatalyst, characterized in that : The CoFe-O-S / NF catalyst is prepared using cobalt-iron Prussian blue analog as a template through calcination treatment and special hydrothermal sulfidation treatment with hydrazine hydrate. SEM morphology shows that after special sulfidation, CoFe-PBA transforms from cubic blocks into a nanosheet structure, and the results of X-ray powder diffraction experiments demonstrate the complete success of sulfidation.

2. A method for preparing a CoFe-O-S / NF material, comprising the following steps: (1) Preparation of CoFe-PBA / NF: Potassium ferricyanide, trisodium citrate, and cobalt nitrate are mixed in an aqueous solution and stirred at room temperature to react, obtaining CoFe-PBA / NF. (2) Preparation of CoFe-O / NF: The precursor CoFe PBA / NF is heat-treated in a muffle furnace at different temperatures. (3) Preparation of CoFe-O-S / NF: Hydrazine hydrate and sulfur powder are mixed in an aqueous solution in different ratios. The prepared CoFe-O / NF is placed in the mixed solution and transferred to a reaction kettle for hydrothermal reaction. After cooling to room temperature, it is rinsed several times with ethanol and water and dried in an oven to obtain the sample.

3. The preparation method according to claim 2, characterized in that: In step (2), the heat treatment temperature is 200 - 600 °C and the time is 2 - 3 hours.

4. In step (3), the temperature of hydrothermal sulfidation is 120 - 200 °C and the time is 12 - 36 hours.

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