Polyacid derivative, preparation method thereof and water electrolysis hydrogen evolution catalyst

Abstract

The invention provides a polyacid derivative, a preparation method thereof and an electrolytic water hydrogen evolution catalyst, and belongs to the field of electrocatalytic hydrogen evolution materials, and the molecular formula of the polyacid derivative is [Co (NH3) 6] 2 (MnMo9O32). The preparation method comprises the following steps: mixing an aqueous solution of ammonium 9-molybdenum manganate octahydrate with an aqueous solution of cobalt hexammine trichloride, reacting at 70-90 DEG C for 2-5 hours, filtering, washing, and freeze-drying to obtain [Co (NH3) 6] 2 (MnMo9O32). According to the present invention, the polyacid derivative is adopted as the precursor, and the hydrothermal reaction and the H2-Ar atmosphere calcination are combined so as to achieve the efficient preparation of the electrolytic water hydrogen evolution catalyst Co4S3-MnS-MoS2 (at) CC, such that the electro-catalytic performance of the catalyst is significantly improved;

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic hydrogen evolution materials, and specifically relates to polyoxometalate derivatives, their preparation methods, and electrolytic water hydrogen evolution catalysts. Background Art

[0002] With the increasing global energy demand, the depletion of traditional fossil fuels and environmental pollution problems are becoming increasingly serious. As an efficient and clean energy carrier, the development and utilization of hydrogen energy have become a research hotspot in the energy field. The electrochemical hydrogen evolution reaction (HER) is a key technology for producing high-purity hydrogen, and the research and development of high-performance electrocatalysts are the core of realizing efficient electrolytic water. At present, although noble metal-based catalysts (such as platinum) have excellent performance, their scarcity and high cost limit large-scale applications. Therefore, the development of low-cost and high-performance non-noble metal catalysts is of great significance. Polyoxometalate compounds are considered a potential electrocatalytic material due to their unique redox ability and structural diversity. However, the stability and conductivity of polyoxometalate-based catalysts in the prior art still need to be improved. Traditional technologies for preparing metal sulfides have problems such as uneven mixing of reaction raw materials, asynchronous reactions, inconsistent product morphologies, and easy agglomeration, as well as different nucleation rates of free metal salts during the hydrothermal process, resulting in poor electrocatalytic hydrogen evolution performance. Therefore, the development of a more efficient and stable electrolytic water hydrogen evolution catalyst is of great significance. Summary of the Invention

[0003] In view of the technical problems existing in the background art, the present invention provides polyoxometalate derivatives, their preparation methods, and electrolytic water hydrogen evolution catalysts, aiming to solve the problems of low efficiency and poor stability of existing electrocatalysts, especially the high cost of noble metal catalysts and the insufficient conductivity of traditional transition metal sulfide catalysts.

[0004] In the first aspect, the present invention provides a polyoxometalate derivative with the molecular formula [Co(NH3)6]2(MnMo9O 32 ).

[0005] In the second aspect, the present invention provides a preparation method of a polyoxometalate derivative, comprising the following steps: Mix an aqueous solution of ammonium manganese nonamolybdate octahydrate with an aqueous solution of hexaamminecobalt(III) chloride, react at 70-90 °C for 2-5 h, and obtain [Co(NH3)6]2(MnMo9O 32 ) after filtration, washing, and freeze-drying.

[0006] Preferably, the pH of the aqueous solution of ammonium manganese nonamolybdate octahydrate is adjusted to 2-4; the concentration of the aqueous solution of ammonium manganese nonamolybdate octahydrate is 6-8 mmol / L.

[0007] In the embodiment of the present invention, the preparation method of ammonium manganese nonamolybdate octahydrate comprises the following steps: Dissolve ammonium heptamolybdate in deionized water, adjust the pH to 4 - 6 with glacial acetic acid, add manganese sulfate solution, stir and heat to boiling. Yellow precipitate appears, then add sodium persulfate solution, heat to 80 °C. The solution turns orange - red. Maintain this temperature for 30 - 40 min, then let it stand overnight at room temperature. Orange - red crystals precipitate. After suction filtration, washing, and air - drying, a crude product is obtained. Recrystallization is carried out to obtain ammonium nonamolybdomanganate octahydrate.

[0008] Preferably, the concentration of the aqueous solution of hexaamminecobalt(III) chloride is 50 - 60 mmol / L.

[0009] Preferably, the molar ratio of ammonium nonamolybdomanganate octahydrate to hexaamminecobalt(III) chloride is 1:2.

[0010] Preferably, the temperature of freeze - drying is - 40 - 60 °C, and the time of freeze - drying is 24 - 48 h.

[0011] In a third aspect, the present invention provides an application of a polyacid derivative in the preparation of an electrocatalytic hydrogen evolution catalyst for electrolytic water.

[0012] In a fourth aspect, the present invention provides a preparation method of an electrocatalytic hydrogen evolution catalyst for electrolytic water, comprising the following steps: Dissolve [Co(NH3)6]2(MnMo9O 32 ) and thiourea in water, add carbon cloth, react at 180 - 200 °C for 18 - 24 h. After cooling, take out the carbon cloth, wash it, dry it. Place the dried carbon cloth in a H2 - Ar mixed gas, heat it to 450 - 550 °C and calcine for 2 - 4 hours to obtain the Co4S3 - MnS - MoS2@CC electrocatalytic hydrogen evolution catalyst for electrolytic water.

[0013] Preferably, the molar ratio of [Co(NH3)6]2(MnMo9O 32 ) to thiourea is 1:(40 - 60).

[0014] Preferably, the heating rate is 3 - 5 °C / min.

[0015] Preferably, the volume fraction of hydrogen in the H2 - Ar mixed gas is 5%. Using the H2 - Ar mixed gas for calcination can keep the metal elements in a low valence state, so that the material is more stable in the hydrogen evolution reaction (HER).

[0016] In a fifth aspect, the present invention provides an electrocatalytic hydrogen evolution catalyst for electrolytic water prepared by the above - mentioned preparation method of an electrocatalytic hydrogen evolution catalyst for electrolytic water.

[0017] In the present invention, the polyoxoacid derivative used as a precursor can integrate various transition metal elements at the molecular level, providing structural diversity for catalyst preparation. In the prepared Co4S3-MnS-MoS2@CC composite electrocatalyst, there are high charge transfer rates, rich heterostructure interfaces and efficient diffusion channels among the components. The doping of a small amount of Co4S3 and MnS not only promotes charge transfer, but also the unique morphology formed increases the surface area of the catalyst, providing rich surface active sites. In addition, this composite structure enables the catalyst to maintain excellent long-term stability and tolerance in different pH solutions, thus significantly improving the overall water electrolysis performance and preparing a composite electrode material suitable for efficient water electrolysis.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows; The present invention synthesized a new polyoxoacid derivative [Co(NH3)6]2(MnMo9O 32 ) (denoted as Co2MnMo9), and used it as a precursor to prepare a hydrogen evolution catalyst for water electrolysis. Through a process combining hydrothermal reaction and calcination in an H2-Ar atmosphere, the efficient preparation of the composite material was realized. This method avoids the performance differences caused by uneven mixing of multiple metal sources in traditional methods and significantly improves the electrocatalytic performance of the catalyst. The Co4S3-MnS-MoS2@CC composite electrocatalyst prepared from the polyoxoacid derivative [Co(NH3)6]2(MnMo9O 32 ) as a precursor exhibits an extremely low overpotential (88 mV, 1 mA·cm - ²) and excellent long-term stability in a 1 M KOH electrolyte. Moreover, the present invention uses inexpensive transition metal elements and a simple synthesis method, avoiding the use of precious metals, reducing costs, and at the same time reducing the impact on the environment. Description of the Drawings

[0019] Figure 1 It is the infrared spectrum of the polyoxoacid derivative Co2MnMo9 prepared in Example 1 of the present invention and its raw materials; Figure 2 is the EDS elemental analysis of the polyoxoacid derivative Co2MnMo9 prepared in Example 1 of the present invention. Among them, Figures 2(a) and 2(b) are the elemental analysis diagrams of different positions of Co2MnMo9; Figure 3 It is the XRD patterns of Co4S3-MnS-MoS2@CC prepared in Example 2 of the present invention and MnS-MoS2@CC prepared in Comparative Example 1; Figure 4 It is the XPS diagram of Co4S3-MnS-MoS2@CC prepared in Example 2 of the present invention; Figure 5SEM image of Co4S3-MnS-MoS2@CC prepared in Example 2 of the present invention; Figure 6 is the morphology test and elemental analysis spectrogram of Co4S3-MnS-MoS2@CC prepared in Example 2 of the present invention; among which, Figure 6(a) is the TEM image, Figures 6(b) and 6(c) are the HRTEM images, and Figure 6(d) is the elemental distribution spectrogram; Figure 7 LSV curves, Cdl curves and Tafel curves of Co4S3-MnS-MoS2@CC prepared in Example 2 of the present invention, MnS-MoS2@CC prepared in Comparative Example 1, and MoS2@CC prepared in Comparative Example 2 under alkaline conditions (a-c) and acidic conditions (d-f) respectively; Figure 8 Comparison diagram of polarization curves of Co4S3-MnS-MoS2@CC prepared in Example 2 of the present invention before and after 5000 CV cycles, and long-term durability test diagrams under acidic and alkaline conditions respectively; Figure 9 Synthesis schematic diagram of Co4S3-MnS-MoS2@CC material in Example 2 of the present invention. Detailed implementation manners

[0020] Embodiments of the technical solution of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0021] For those not specified in the embodiments in terms of specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not specified in terms of the manufacturer, they are all conventional products that can be obtained through commercial purchase or commonly used in this field.

[0022] Example 1 Synthesis of [Co(NH3)6]2(MnMo9O 32 ) polyoxometalate derivative (NH4)6[MnMo9O 32 ·8H2O (denoted as MnMo9) synthesis: First, weigh 1 mmol ammonium heptamolybdate and dissolve it in 10 mL deionized water, adjust the pH to 5.1 with glacial acetic acid, then dissolve 7 mmol manganese sulfate in 10 mL deionized water, mix the above two solutions, stir and heat to boiling, and yellow precipitate appears. Continue to weigh 2 mmol sodium persulfate and dissolve it in 5 mL water, add it to the above mixed solution, heat to a solution temperature of 80 °C, the solution turns orange-red, keep this temperature for 30 minutes, then place it at room temperature overnight until orange-red crystals precipitate, filter by suction, wash, and air-dry to obtain the crude product, and perform recrystallization 3 times to obtain the crystalline product MnMo9.

[0023] Synthesis of [Co(NH3)6]2(MnMo9O 32 ): Weigh 0.3 mmol of MnMo9 and dissolve it in 40 mL of deionized water to form an orange-red solution (Solution 1), and adjust the pH to 3.0 with dilute hydrochloric acid. Dissolve 0.6 mmol of [Co(NH3)6]Cl3 in 10 mL of distilled water to form a light yellow solution (Solution 2). Slowly add Solution 2 to Solution 1 under stirring, and heat the mixed solution to 80 °C and keep it at a constant temperature for 2 hours. After the reaction, repeatedly rinse the precipitate with deionized water and ethanol, and obtain the target product [Co(NH3) · 6]2(MnMo9O 32 )(denoted as Co2MnMo9) through freeze-drying for 24 hours.

[0024] Example 2 Preparation of Co4S3-MnS-MoS2@CC electrocatalytic hydrogen evolution catalyst Dissolve 0.5 mmol of Co2MnMo9 prepared in Example 1 and 25 mmol of thiourea in 35 mL of deionized water, stir for 2 hours, transfer the solution to a reaction kettle, add a carbon cloth with a geometric area of 3×2 cm² as the conductive substrate, and react at 200 °C for 24 hours. After the reaction, transfer the reaction kettle to the fume hood to open it, take out the carbon cloth, wash and dry it. Place the dried carbon cloth in a H2-Ar mixed gas (hydrogen content 5%), heat it to 500 °C at a heating rate of 5 °C / min, and keep this temperature for calcination for 2 hours to obtain the target product denoted as Co4S3-MnS-MoS2@CC.

[0025] The synthesis schematic diagram of the Co4S3-MnS-MoS2@CC material in this example is as Figure 9 shown.

[0026] Comparative Example 1 Synthesis of MnS-MoS2@CC Synthesis of MnS-MoS2@CC: Dissolve 0.5 mmol of MnMo9 prepared in Example Ⅰ and 25 mmol of thiourea in 35 mL of deionized water, stir for 2 hours, then transfer the solution to a reaction kettle, add a carbon cloth with a geometric area of 3×2 cm², and react at 200 °C for 24 hours. After the reaction, transfer the reaction kettle to the fume hood to open it, take out the carbon cloth, wash and dry it. Place the dried carbon cloth in a H2-Ar mixed gas (hydrogen content 5%), heat it to 500 °C at a heating rate of 5 °C / min, and keep this temperature for calcination for 2 hours to obtain MnS-MoS2@CC.

[0027] Comparative Example 2 Synthesis of MoS2@CC Synthesis of MoS2@CC: 0.5 mmol of ammonium molybdate and 25 mmol of thiourea were dissolved in 35 mL of deionized water at room temperature. A carbon cloth with a geometric area of 3×2 cm² was added, and the mixture was hydrothermally treated at 150 °C for 8 h. After the reaction, the autoclave was transferred to a fume hood and opened. The carbon cloth was taken out, washed, and dried. The dried carbon cloth was placed in a H2-Ar mixed gas (hydrogen content 5%) and heated to 500 °C at a heating rate of 5 °C / min, and calcined at this temperature for 2 hours to obtain MoS2@CC.

[0028] Performance Test 1. Material Characterization Test Figure 1 The infrared spectra of the polyoxometalate derivative Co2MnMo9 prepared in Example 1 and its raw materials were obtained. Infrared spectroscopy analysis was performed on the polyoxometalate before and after cation exchange, and compared with the infrared spectrum of [Co(NH3)6]Cl3. The results showed that in the infrared spectrum of Co2MnMo9, in addition to retaining the characteristic peaks of 3+ and [MnMo9O 32 6- , the peak originally belonging to the cation NH 4+ in the polyoxometalate MnMo9 (1400 cm -1 ) disappeared, and at the same time, the symmetric bending vibration peak of the N-H bond belonging to [Co(NH3)6] 3+ (1300 cm -1 ) appeared. In addition, the peak of the target product at 3280 cm -1 was narrower in width and shifted to a higher wavenumber compared to the characteristic peak of NH 4+ , indicating the effectiveness of the cation exchange strategy. Figures 2(a) and 2(b) are EDS elemental analysis diagrams of different positions of the polyoxometalate derivative Co2MnMo9 prepared in Example 1. The results showed that the ratio of the three metal elements Co, Mn, and Mo was close to 2:1:9. In summary, these results confirmed the successful synthesis of [Co(NH3)6]2(MnMo9O 32 ) and provided an important basis for subsequent research.

[0029] Figure 3 The XRD patterns of Co4S3-MnS-MoS2@CC prepared in Example 2 and MnS-MoS2@CC prepared in Comparative Example 1 are shown as Figure 3 ​As shown in Figure 2, the diffraction peaks at 30.0°, 31.4°, 47.9°, 52.5°, 73.6°, and 77.0° are attributed to the (311), (222), (511), (400), (731), and (800) crystal planes of Co4S3 (PDF#02-1338). In addition, the diffraction peaks at 25.8°, 49.3°, and 69.8° are attributed to the (100), (103), and (203) crystal planes of MnS (PDF#40-1289). The remaining diffraction peaks are concentrated at 14.1°, 33.3°, 39.6°, 49.8°, and 58.9°, which correspond to the (002), (101), (103), and (110) crystal planes of MoS2@CC (PDF#37-1492) prepared in Comparative Example 2.

[0030] Figure 4 This is the XPS graph of Co4S3-MnS-MoS2@CC prepared in Example 2. It was characterized by XPS and its chemical composition and different element valence states were further studied. The complete XPS spectrum of Co4S3-MnS-MoS2@CC detected six elements: Co, Mn, O, Mo, C and S. The C element obtained is irrelevant and can be used as a calibration reference. For the catalyst Co4S3-MnS-MoS2@CC, the Co 2p spectrum shows that the Co element in the composite material has two oxidation states. The four peaks at 797.9 eV, 794.1 eV, 781.7 eV and 779.0 eV are respectively attributed to Co 2+ 2p 1 / 2 、Co 3+ 2p 1 / 2 、Co 2+ 2p 3 / 2 and Co 3+ 2p 3 / 2 The two peaks at 802.1eV and 785.4eV are also related to Co 2+ and Co 3+ The two satellite peaks correspond to each other. Mn has only one oxidation state, namely Mn 2+ 2p 1 / 2 and Mn 2+ 2p 3 / 2 In the Mo 3d spectrum ( Figure 4 (d)), the binding energies at 232.9 eV and 229.8 eV are similar to those of Mo 4+ 3d 3 / 2 and Mo 4+ 3d 5 / 2Consistency proves that the valence state of Mo element in the catalyst is +4. Moreover, the peak at 226.9 eV corresponds to S 2s of the Mo-S bond, further proving the existence of MoS2 phase in the composite material. The two weak peaks at 236.0 eV and 232.8 eV of Mo 3d are due to the presence of MoO3, indicating that MoS2 is slightly oxidized during the preparation process. In the high-resolution XPS spectrum of S 2p ( Figure 4 (e)), the two peaks at 163.7 eV and 162.5 eV point to S 2p 1 / 2 and S 2p 3 / 2 . It further proves the composition of the metal sulfide. Observing the O 1s orbital, a weak oxidation peak appears at 530.7 eV, attributed to the small amount of MoO3 present in the sample. Additionally, a strong peak appears at 532.2 eV, which is formed by the adsorption and dissociation of water molecules on the sample surface.

[0031] Figure 5 Figures 5 and 6 show the morphology and element distribution of Co4S3-MnS-MoS2@CC prepared in Example 2 at different magnifications in scanning electron microscopy and transmission electron microscopy. It can be found that the Co4S3-MnS-MoS2@CC particles prepared in Example 2 are tiny and present a uniformly dispersed nano-petal shape. And Figure 6(d) shows that a small amount of Mn (1.52%) and Co (1.69%) elements and a large amount of Mo (21.39%) elements are uniformly dispersed in the Co4S3-MnS-MoS2@CC heterostructure.

[0032] 2. Electrochemical performance test The electrochemical test was carried out on a CHI760E electrochemical workstation. The electrocatalytic performance of the material was tested using a three-electrode system: the reference electrodes were Hg / Hg2Cl2 (in 0.5 M H2SO4) and Hg / HgO (in 1 M KOH), the counter electrode was a graphite rod, and the working electrode was the modified carbon cloth with a test area of 1 cm×1 cm.

[0033] Figure 7 LSV curves, Cdl curves and Tafel curves of Co4S3-MnS-MoS2@CC prepared in Example 2, MnS-MoS2@CC prepared in Comparative Example 1 and MoS2@CC prepared in Comparative Example 2 under alkaline conditions (a - c) and acidic conditions (d - f). Under alkaline conditions, the overpotentials of Example 2, Comparative Example 1 and Comparative Example 2 at 10 mA·cm -2 are 88 mV, 182 mV and 197 mV respectively. The Cdl values are 66.20 mF·cm -2 , 57.81 mF·cm -2 and 25.37 mF·cm-2 The Tafel slopes are 64.10 mV·dec -1 , 88.05 mV·dec -1 and 183.42 mV·dec -1 . Under acidic conditions, the overpotentials of Example 1, Comparative Example 1 and Comparative Example 2 at 10 mA·cm -2 are 140 mV, 188 mV and 237 mV respectively, and the Cdl values are 47.45 mF·cm -2 , 37.35 mF·cm -2 and 11.97 mF·cm -2 respectively. The Tafel slopes are 70.56 mV·dec -1 , 88.05 mV·dec -1 and 183.42 mV·dec -1 . Experimental data show that Co4S3-MnS-MoS2@CC (Example 2) exhibits significantly better electrocatalytic performance than the comparative examples (MnS-MoS2@CC and MoS2@CC) under both alkaline and acidic conditions. At a current density of 10 mA·cm - ², its alkaline overpotential (88 mV) and acidic overpotential (140 mV) are much lower than those of the comparative examples, and at the same time, it has a higher Cdl value (66.20 mF·cm - ² for alkaline condition, 47.45 mF·cm - ² for acidic condition) and a lower Tafel slope (64.10mV·dec - ¹ for alkaline condition, 70.56 mV·dec - ¹ for acidic condition), indicating a larger electrochemically active surface area and faster reaction kinetics. The introduction of Co4S3 optimizes the electronic structure through multi-component synergistic effects, increases the exposure of active sites, and accelerates the charge transfer and intermediate conversion processes, significantly improving the electrocatalytic efficiency.

[0034] Figure 8 Figure for comparing polarization curves of Co4S3-MnS-MoS2@CC prepared in Example 1 before and after 5000 cycles of CV shows that the stability of this catalyst is very good. In addition, at a test voltage of 330 mV, the long-term durability is tested by chronoamperometry at constant voltage for 33 hours, and it can be found that this catalyst has excellent long-term durability at high voltages.

[0035] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and embodiments having the same constitution and achieving the same effects within the technical scope of the present invention are included in the technical scope of the present invention. In addition, within the scope not departing from the gist of the present invention, various modifications that can be conceived by those skilled in the art to the embodiments, and other forms constructed by combining some constituent elements of the embodiments are also included in the scope of the present invention.

Claims

1. A polyoxometalate derivative, characterized in that, The molecular formula of the polyoxoacid derivative is [Co(NH3)6]2(MnMo9O 32 ).

2. The preparation method of the polyoxoacid derivative according to claim 1, characterized in that, Comprising the following steps: Ammonium nonamolybdomanganate octahydrate is provided. An aqueous solution of ammonium nonamolybdomanganate octahydrate is mixed with an aqueous solution of hexaamminecobalt(III) chloride and reacted at 70 - 90 °C for 2 - 5 h. After filtration, washing and freeze-drying, [Co(NH3)6]2(MnMo9O 32 ) is obtained.

3. The preparation method of the polyoxoacid derivative according to claim 2, characterized in that, Adjust the pH of the aqueous solution of ammonium nonamolybdomanganate octahydrate to 2 - 4; the concentration of the aqueous solution of ammonium nonamolybdomanganate octahydrate is 6 - 8 mmol / L; the concentration of the aqueous solution of hexaamminecobalt(III) chloride is 50 - 60 mmol / L.

4. The preparation method of the polyoxoacid derivative according to claim 2, characterized in that, The molar ratio of ammonium nonamolybdomanganate octahydrate to hexaamminecobalt(III) chloride is 1:

2.

5. The preparation method of the polyoxoacid derivative according to claim 2, wherein The temperature of freeze-drying is -40~-60 °C, and the time of freeze-drying is 24~48 h.

6. Use of the polyoxometalate derivative according to claim 1 in the preparation of an electrocatalytic water splitting hydrogen evolution catalyst.

7. A preparation method of an electrolytic water hydrogen evolution catalyst, characterized in that, Comprising the following steps: Using the polyoxoacid derivative described in claim 1 as a precursor, dissolve the [[Co(NH3)6]2(MnMo9O 32 ) and thiourea in water, add carbon cloth, react at 180 - 200 °C for 18 - 24 h, cool down and take out the carbon cloth, wash and dry it. Place the dried carbon cloth in a H2 - Ar mixed gas, heat it up to 450 - 550 °C and calcine for 2 - 4 hours to obtain the Co4S3 - MnS - MoS2@CC electrocatalyst for hydrogen evolution in water electrolysis.

8. The preparation method of the electrolytic water hydrogen evolution catalyst according to claim 7, characterized in that, The molar ratio of [Co(NH3)6]2(MnMo9O 32 ) to thiourea is 1:(40 - 60).

9. The preparation method of the electrolytic water hydrogen evolution catalyst according to claim 7, wherein The heating rate for heating to 450~550 °C is 3~5 °C / min.

10. An electrocatalytic water splitting hydrogen evolution catalyst prepared by the method for preparing an electrocatalytic water splitting hydrogen evolution catalyst according to any one of claims 7~9.

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